Finned primary surface heat exchanger

ABSTRACT

A heat exchanger composed of primary-surface heat exchange channel elements, each element being formed and bound by a thermally conductive material and having slotted secondarysurface fins disposed substantially along its longitudinal length. The fins, along with the slatted apertures on the fins, are oriented to provide a substantial through-flow area for an external fluid which in the operating mode will flow through passages formed between adjacent channel elements.

United States Patent 1191 Kun [ 1 Nov. 5, 1974 FINNED PRIMARY SURFACEHEAT EXCHANGER Inventor: Leslie C. Kim, Williamsville, NY.

.Union Carbide Corporation, New York, NY.

Filed: July 10, 1972 Appl. No.: 270,259

Assignee:

US. Cl. .165/148, 29/1573 Int. Cl. F28b l/14 Field of Search 165/130,131, 151-153,

References Cited UNITED STATES PATENTS Heuer et al. 165/170 Keith165/170 Beck 165/151 FOREIGN PATENTS OR APPLICATIONS 1,521,499 3/1968France 165/151 1,324,178 3/1963 France ..165/130 PrimaryExaminer-Charles J. Myhre Assistant ExaminerTheophil W. Streule, Jr.Attorney, Agent, or Firm-John C. LeFever [57] ABSTRACT A heat exchangercomposed of primary-surface heat exchange channel elements, each elementbeing formed and bound by a thermally conductive material and havingslotted secondary-surface fins disposed substantially along itslongitudinal length. The fins,

10 Claims, 21 Drawing Figures PATENTEBHuv SIGN 3,845,8 SIIEU 1 WPATENTEUHIJY 5:914

SIIEH is N 6 Steam in Condensate H 0 out PATENTEDHUY 5 m4 SNEEF 50$ 5'PATENTEUHUV 5m IIOO- AIR VOLUME FLOWRATE/FT2 FRONTAL AREA FT /MlN/FT 1FINNED PRIMARY SURFACE HEAT EXCHANGER FIELD OF THE INVENTION BACKGROUNDOF THE INVENTION There is an increasing need in industry for compact,light weight heat exchangers capable of transferring large amounts ofheat from one medium to a second medium. For example, the increased useof superconductive devices and maser applications have placed a demandfor the development of heat exchangers for cryogenic environments. Theneed for reliable, rugged and compact heat exchangers, for operation insystems at ambient temperatures and above, has also increased. One ofthe major industries that is constantly searching for a compact, lightweight heat exchanger for its combustion engines, is the automobileindustry. Various types and styles of radiators have been designed, suchas the individually finned round tubes, the hexagonshaped air tubes withWater passages between the tubes, and the flat dimpled water tubes withair flow therebetween. The pre-l942 automobile engines were designed todeliver between 50 and 125 horsepower, and radiators designed for usewith them were designed to operate close to atmospheric pressure. Asimple solder joined finned-copper constructed radiator was thereforesufficient to cool the low horsepower engine of the automobile withoutmuch of a threat of overheating. Various copper radiators havingcup-like or frustroconical surface projections have been designed duringthis pre-l942 period but the finned copper radiator proved moresuccessful and suitable for automobile applications. I

The automobile industry, however, in the post-1945 era embarked upon thedesign of high power rated engines while simultaneously attempting tocompact them as much as possible. This dual design approach coupled tothe employment of improved lubricants resulted in an internal combustionengine capable of operating at high permissible temperatures. To satisfythe heat transfer requirements of such compact high power rated engines,and to avoid loss of coolant, the tube and inherent in soft solderathigh temperatures, such solder being the'securing medium between thetubes and fins LII fin copper radiators were designed to operate underpressure so as to increase the boiling temperature of the coolant.However, within the last several years, additional power operatedequipment, such as air conditioners and the like, was added to theautomobile thereby further increasing the demands on the internalcombustion engine and consequently the duty of the heat rejectionsystem. This has necessitated the designing of present day radiators tooperate at pressures as high as 15 psig. to prevent coolant loss andoverheating. The operating temperature of the automobile engine isanticipated to rise further in the near future thereby necessitating aheat transfer system operable with existing coolants under still higherpressure conditions. The conventional type finned-copper radiator willnot perform satisfactorily in an increased temperature environment dueto the low stress characteristics of the radiator. In addition, thesteady increase in the price of copper is causing copper to become anundesirable material for radiator applications from an economicalstandpoint.

In heat exchange applications requiring pressurebearing walls as theprimary heat exchange surface, new designs have recently been developedwhereby thermally conductive thin material can be fabricated intochannels having isocompression supports or trucated conicalwall-supporting projections. The channels can be aligned in juxtaposedrelationship to form a compact light weight heat exchanger having afirst set of passages defined by, and bound within, the conductive wallsof each channel, and a second set of passages defined by, and disposedbetween, the juxtaposed channels so that a first medium can be fedthrough one set of passages while a second cooler medium can be fedthrough the other set of passages thereby effecting a heat exchangebetween the mediums without having the mediums intermix. The specificdetails of these compact, economical channelized heat exchangers can befound in applicants copending patent application Serial No. 189,659titled Primary Surface Heat Exchanger and Manufacture Thereof, now US.Pat. No. 3,757,856, granted Sept. 11, 1973 and in copending patentapplication Ser. No. 189,509 titled Primary Surface Heat Exchanger, byL. C. Kun and J. B. Wulf, now US. Pat. No. 3,757,855 granted Sept. ll,1973. Also in copending application Ser. No. 344,429 titled Cross FlowHeat Exchanger now US. Pat. No. 3,810,509 granted May 14, 1974.

The present invention is directed'to an improvement on all types ofchannelized primary-surface heat ex-' changers, whether stayed by meansof numerous support members or by wall-supporting projections, theimprovement being the addition of one or more slotted fins disposedalong the longitudinal edge of each channel in such a manner that itprovides an efficient compact heat exchanger that is economical toconstruct primarily because it offers a substantial reduction in weightthrough optimum metal utilization.

SUMMARY OF THE INVENTION The heat exchanger of this invention basicallycomprises at least one primary-surface heat exchange channel elementformed and bound by at least one thermally conductive metal or plasticwalled material, said element having an entrance opening and an exitopening, the improvement which comprises the addition of at least onesecondary-surface heat exchange slotted fin disposed substantially alongat least one longitudinal section of the channel element and whereinsaid slotted fin has a multitude of slatted apertures arranged in alouver configuration. The fins primarily extend outward from thelongitudinal segment of the element at an angle made with a planecontaining the maximum dimensional width line of, and the longitudinaldimensional length line of, said element to provide a multitude ofslatted apertures in said fin when viewed in a direction parallel to theplane so defined. At least two of such channels, when aligned injuxtaposed relationship, or otherwise appropriately stayed, will form aheat exchanger having a first set of passages defined by, and boundwithin, the conductive walls of each channel, and a second set ofpassages defined by, and disposed between adjacent channels so that afirst medium can be fed through one set of passages while a secondcooler medium can be fed through the other set of passages therebyeffecting a heat exchange between the mediums without having the mediumsintermix.

For circular channels or tubes, the maximum dimensional width line shallmean the diameter of the tube taken along a line containing the finattachment point on the tube. When a tube has more than one fin, themaximum dimemsional width line shall mean the diameter of the tube takenalong a line where the medium arithmetic mean distance of fin attachmentpoints onto one side of the line from one half of the tube will be equalto the minimum arithmetic mean distance of the fin attachment pointsonto the other side of the line from the other half of the tube. For anarray of two or more circular tubes, the maximum dimensional width lineshall mean the diameter of the tube taken in plane perpendicular to aplane containing the center points of two adjacent tubes and thelongitudinal axis of the tube.

The term primary-surface heat exchanger refers to heat exchangerswherein substantially all the material which conducts heat between twomedia comprises the walls separating the two media. In contrast,secondary surface heat exchangers contain a substantial amount ofmaterial in the form of fins which do not separate the media but arecontacted on virtually all surfaces by a single medium. In addition, inprimary surface heat heat exchanger applications wherein a pressuredifference exists between the two media of the system, substantially allof the heat exchanger material is stressed pneumatically. Stated anotherway, primary surface heat exchanger refers to a heat exchangerconsisting primarily of plates or sheets and having no separate oradditional internal or external members, such as fins, so that theexchanger is constructed of plates or sheets each side of which is incontact with a different fluid, and heat transfer is substantially anddirectly between the plates and the fluid.

The term channel element refers to any enclosed longitudinal memberhaving an entrance opening and an exit opening, and formed and bound byat least one thermally conductive metal or plastic wall material.Channels elements could be of the isotension, isocompression, ortruncated projected type as specified in the above-mentioned patentapplications, or be of the outwardly dimpled tubular types as disclosedin U.S. Pat. Nos. 1,540,9l3 and 1,413,163, or of the outwardly dimpledrectangular passages as disclosed in U.S. Pat. Nos. l,64l,l48 and2,354,865. The channel elements could be spaced apart by wall projectedsupports, by wire members, by epoxy or epoxy coated washers, byappropriately bent channels or alternately bent channels, by metal orplastic strips, or by any other conventional means.

The slotted tins can be disposed on the longitudinal aft and foresections of the channel as defined by the direction of a medium flowthrough passages formed between adjacent channels, or otherwise definedas the remote sections of the channel as measured from a planecontaining the center points of two adjacent channels and thelongitudinal axis of the channel. The elongated slots or slattedapertures can be disposed perpendicular to the longitudinal length ofthechannel, but, however, when so arranged, the fins would have to be bentat a fin angle 7 of about 90 with respect to a plane containing themaximum dimensional width line of, and the longitudinal dimensionallength line of, the channel, if the slats in the fins are to be alignedto provide a minimum air flow path on the slats for a medium flowingthrough passages formed between adjacent channels, since such a designwould provide maximum heat transfer. If substantial overlapping of thefins is to be avoided in an array of channels aligned parallel to thedirection of flow of a medium between the channels, then the width of aorientated fin will dictate the spacing between the channels. Sincecompactness is a desirable characteristic in a heat exchanger, the finshould preferably be disposed at an angle 7 of less than 90 with respectto the plane containing the maximum dimensional width line, andlongitudinal dimensional length line of the channel. On the otherextreme, this fin angle 'y can be 0 even though the fins would bedisposed such that the slatted apertures would be substantially alignedparallel to the directional flow of a medium between adjacent channels,since in certain respects, this configuration may be desirable from aneconomical or mechanical viewpoint. Thus the fin angle 7, formed betweenthe plane of the fin and the plane containing the maximum width andlongitudinal lines of the channel, can be between about 0 and 90, butpreferably between about 0 and about 60. For a given fin bending angle'y, the slot angle a, formed by the longitudinal length line ofthechannel and the longitudinal length line of the slot, and the slat angle,8, formed by the plane of the fin and the plane of the slat memberbetween adjacent slatted apertures, would have to be chosen to providesubstantially minimum fin frontal area" and thus substantially maximumarea of the slatted aperture orientated normal to the flow of a mediumthrough passages between adjacent channels. Fin frontal area" is definedas the area of the projection of the entire array of fins onto a planenormal to the direction of flow of a medium through passages formedbetween adjacent channels. The slot angle a can vary broadly from 0 toas measured clockwise from the longitudinal axis of the channel to thelongitudinal length line of the slot. Preferably the slot angle a shouldbe 90i45 for most applications since this would provide a sufficientuninterrupted flow path on the fin extending outward from the attachedsegment points on the channel. The slat angle B can vary between about15 and about 90 for most applications although an angle between about 30and about 60 would be preferable since it would provide sufficientslatted apertures which can be obtained through one shot of a die or thelike, thus minimizing the manufacturing cost. An angle ,8 ofless thanabout 15 would be insufficient since it would not provide an adequateopening between adjacent slats due to finite material thickness of thefins.

The width of the slats of the louver constructed fins should be smallerthan about 0.250 inch for most applications, although a slat width ofless than 0.10 inch would be desirable. For the lower limit, the slatwidth should be at least 0.02 inch and preferably at least about 0.03inch. The smaller the slat width, the smaller the flow path length onthe slat for a medium passing through the apertures in a louverconstructed fin. Usually finite fin thickness limits the minimum widthdimension for the slat of a louver constructed fin.

As specified above, the orientation of the fins, slats and slattedapertures can be defined by the angles 7, a,

and B. The interrelation of these three angles can be expressed asfollows:

sin 6=cosB siny-cos7sinflcosa (I) where 0 is the angle of approachdefined as the angle between a first line which is parallel to the planecontaining the maximum dimensional width line and the longitudinaldimensional length line of'the channel, and perpendicular to thechannels longitudinal length line, and a second line formed by theintersection of a plane onto the surface of the slat where said plane isnormal to the surface of the slat and contains said first line asdefined above.

Thus we see that for any angle y, a or [3, the remaining two angles canvary widely for a specific angle of approach 6 for a particular heatexchange operational mode. By first selecting an angle of approach0,-and then selecting a fin bending angle 'y to accommodate a specificarray of channels in an overall heat exchanger configuration, the slatangle B and the slot angle a can be substantially varied, and stillsatisfy the solution of Equation l. However, once one of these angles isselected, while maintaining y and t9 constant, the other angle becomesfixed according to the Equation I. It is thus shown that y, a and B canvary widely but they are interrelated in accordance with Equation Iwhich defines the angle of approach which can be selected for aparticular application. An angle of approach 0 of about 60 or less wouldbe acceptable for most applications employing the fin arrangement ofthis invention, although an angle of approach 0 of about 0 to about 45would be preferable. As can be seen by Equation I, once you choose oneof the angles 7 a or ,8, while keeping the angle of approach 0 constant,then the other two angles can not be selected independently.Consequently, to provide a desirable fin frontal area for a particularapplication, the angle of approach 0, fin bending angle y, the slatangle B and the slot angle a, all of which are related in accordancewith Equation I, should be picked so that the plane of each slat will besubstantially aligned such that the air flow path across the slats willbe substantially minimized.

The slotted fins can be added both fore and aft of the channel asdefined by the direction of a coolant medium through passages formedbetween adjacent channels, or otherwise defined as the remote sectionsof the channel as measured from a plane containing the center points oftwo adjacent channels and the longitudinal axis of the channel. Thewidth of the fore and aft fins, measured normal to the longitudinallength of the channel, can advantageously be of a different size asdiscovered by James B. Wulf. The maximum dimensional width line of theprimary-surface heat exchange channel can preferably be between about0.5 inch and 3.0 inches for most applications and the width of thesecondary-surface heat exchange fin should be less than about 0.60 inchand preferably wider than 0.l0 inch. For automobile radiatorapplications,'the width of the primary-surface heat exchange element canvary between about 0.75 inch and about 2.0 inches and the width of thesecondary-surface fin can vary from about 0.2 to about 0.5 inches.

The wall material of the primary surface heat exchange channel need notbe highly conductive, although preferably it should be, and can beselected from at least one of the groups consisting of metals, metalalloys, metal clads, ceramics, plastics (such as Mylar), plastic-coatedmetals and the like. The criteria 6 of the material selected for theprimary surface of the channel element is that it be sufficientlythermally conductive so that as a hot medium is passed through thechannel, the heat of the medium will be conducted through the wall ofthe channel to a cooler medium external of, and adjacent to, the channelwhich can absorb the heat thereby successfully effecting a heat transferbetween the mediums without intermixing of said mediums. In addition,the material should preferably be such that it will transmit heatlaterally to the sections where the fins are attached without the needfor a large temperature gradient existing through the material.Materials such as aluminum, copper, steel, zinc, brass, magnesium,titanium, beryllium and Mylar, and the alloy of such material, whereapplicable, are suitable for this application. The wall material of thesecondary-surface heat exchange fin segment must be conductive since itsefficiency is dependent upon its ability to transfer the heat localizedin one area; i.e., in the primary-surface walls; to a cooler area; i.e.,the area external of, and away from, the primary-surface walls; so thatsuch heat can be absorbed by the cooler environment not in contact withthe primary-surface walls. Suitable fin material would include the basemetals and the alloys of aluminum, copper, carbon steel, zinc,magnesium, and beryllium.

An additional modification of the finned primarysurface heat exchangerof this invention would be an arrangement whereby two or more fins wouldbe disposed from the same longitudinal segment on the channel so as toprovide a multiple fin configuration.

The longitudinal mating edges of a channel, along with the fins, whetheror not such fins are an extension of the primary-surface wall materialor are composed of a separate material, can be sealed by conventionaltechniques, i.e., soldering, brazing, welding, or with an adhesivefilled lock-joint to make the channel leak tight. An array of channelsso formed can be suitably spaced apart by wall-supporting projectedbuttons or the like, or by conventional type stayes, to produce acompact, efficient heat exchanger. A pressurized medium, such as hotwater, could then be passed through the channels while a coolant medium,such as cool air, could first pass through the slatted apertures on thelouver type front fin and then pass between, and contact the outersurface of, the primary-surface walls of the channel before exitingthrough the slatted apertures on the rear fin thereby effecting atransfer of heat between the mediums. The fin attached channel could beappropriately bent or curved along its longitudinal length, or shapedinto any curvilinear configuration, to fit the need of anyparticularenvironment.

The slats and/or the fins could also be slightly curved to provide anoptimum type geometry for the heat exchanger in a particular end useapplication.

In a cross-flow heat exchange operational mode, the mediums can be fedthrough their respective passages in a heat exchanger, made according tothis invention, in a perpendicular relationship or at some other anglerelationship therebetween.

DESCRIPTION OF THE DRAWINGS FIG. 1 Isometric view of a heat exchangechannel element of this invention.

FIG. 1A An enlarged sectional view of the heat exchange element of FIG.1 taken along line 1A1A.

FIG. 1B Sectional view of the heat exchange element of FIG. I takenalong line lBlB.

FIG. 1C Sectional view of the heat exchange element of FIG. 1 takenalong line lC-lC.

FIG. ID An enlarged view of slats of the heat exchange element of FIG.1A.

FIG. 1E Alternate embodiment of the heat exchange element of FIG. 1.

FIG. 1F Sectional view of the heat exchange element of FIG. 1 takenalong line 1F-1F.

FIG. 2 Isometric view of heat exchange channel elements having fore andaft fins.

FIG.'2A Sectional view of the heat exchange channel elements of FIG. 2taken'along line 2A2A.

FIG. 2B Sectional view of the heat exchange channel elements of FIG. 2taken along line 2B-2B.

FIG. 3 Isometric exploded view of an automobile radiator employing theheat exchange channel elements of this invention.

FIG. 3A View taken of the longitudinal edge of a heat exchange channelelement of FIG. 3.

FIG. 3B Side view of the heat exchange elements of FIG. 3.

FIG. 3C View taken of the longitudinal edge ofa heat exchange channelelement of FIG. 3.

FIG. 3D Alternate embodiment of the heat exchange elements of FIG. 3.

FIG. 3E Alternate embodiment of the heat exchange elements of FIG. 3.

FIG. 3F Side view of heat exchange elements of FIG. 3 shown without thefins.

FIG. 4 Isometric view of conventional automobile radiator.

FIG. 5 Schematic of test apparatus for checking automobile radiators.

FIG. 6 Schematic of test apparatus for supplying a heated medium throughan automobile radiator.

FIG. 7 Plot of Capacity vs. Volume flowrate for several radiators.

The performance of any heat exchange channelized element can be improvedby adding slotted fins along the longitudinal length of the elementaccording to this invention. FIG. I shows a thin wall isocompressionchannel 1 having a front or fore fin 2 and a rear or aft fin 3. Thedetails of the isocompression channel, including the wall supportingprojections 6, are disclosed in my copending patent application Ser. No.l89,659 now U.S. Pat. No. 3,757,856 granted Sept. II, 1973. Fins 2 and 3extend substantially along the longitudinal edges of channel 1 leavingfinless segments 4 and 5 at opposite ends of channel 1. The finlesssegments 4 and 5 are designed so that when an array of channels aresuperimposed in touching relationship, a vertical support or retainermember 51 can be positioned in touching relationship with the edges ofsaid segments 4 and 5 as shown in FIG. 3. An enlarged sectional view ofchannel 1, FIG. IA, and FIG. 1B, show the various angles y, a, and B atwhich fin 3, along with the slats 7 of the louver type arrangement infin 3, should be orientated so as to provide a multitude of slattedapertures 5 arranged so that the substantially maximum areas of saidapertures 5 are aligned perpendicular to the longitudinal axis ofchannel 1. For a given set of values of y and a, maximum aperture area,as viewed from the flow path of an external medium. will correspond tominimum flow path lengths across slats 7. Fin bending angle y is theangle formed between the plane of the fin 3, and the plane of thechannel continuing both the maximum dimensional width line W and thelongitudinal dimensional line L of channel 1. To minimize momemtum lossin the air flow, the unslotted tip section X (which is provided forstructural strength) should preferably be parallel with the plane of thechannel defined above, or to the directional flow of an external medium.The slot angle a is defined as the angle formed between the longitudinaldimensional line L ofthe slot, and the longitudinal dimensional line Lof channel I. The slat angle B can best be illustrated from FIG. 18where it is shown as the angle formed between the plane of the slat 7and the plane of the overall fin 3. As stated above, the sangle y, a,and B can vary widely depending upon the angle of approach 6 desired. Asstated above, and shown in FIG. 1D, the angle of approach 6 is definedas the angle formed between a line A, which is parallel to the planecontaining lines L and W and perpendicular to the line L, and a line Aformed by the intersection of a plane on the surface of the slat, saidplane being normal to the plane of the slat and containing line A,.Aperture area, as viewed from the flow path of an external medium,approaches a maximum only when the angle of approach 0 has low valuesapproaching 0. Since the heat transfer for a slotted fin is both afunction of the width y of the slats 7, and the length of the slattedapertures L, it would be advisable to first select the slot angle 01 tooptimize the heat transfer characteristics of the fin. The slat angle Bcould next be selected based on the material thickness of the fin and onthe manufacturing feasibility of the fin as based on mechanical andeconomical considerations. Fin bending angle 'y could then easilty bedetermined for an angle of approach 6 suitable for a particular heatrejection system using Equation 1. As stated previously, fin bendingangle 7, slot angle a, and slat angle B, can be varied as long as theysatisfy Equation I for a selected angle of approach 0. By determiningany two of the angles y, a and B, and having a desired angle of approach6, the third angle can be found using Equation I.

FIGS. 1A and 1C show fin bending angle 7, slot angle a and slat angle Bfor front or fore fin 2. Note that the fin bending angle 7 is shown asthe negative of fin bending angle 7 of fin 3. This is not necessary andboth angles may be positive or negative depending on the direction of aand a, and B and B. Likewise, slot angle a and slat angle B could be thesame or different than angles a and B for fin 3. Any artisan candetermine when and if it would be desirable to have different angles ofy, a and B for the front fin 2 as opposed to angles y, a and B for rearfin 3. Preferably, the angles of the front and rear fins including theangle of approach for each fin, should be the same. Economy in thefabrication of the fins alone could dictate the use of the same anglesfor both front and rear fins.

FIG. 1F shows an enlarged side view of the finned heat exchange channel1 of FIG. 1. Fins 2 and 3 are shown with slatted apertures 5, eachformed between slats 7. FIG. 1E shows an alternate embodiment of a heatexchange element 10 having fins 11 and 12 with slots 13 parallel to thelongitudinal length of element 10. The slots 13 can not extendsubstantially along the length of fins l1 and 12 since such a structurewould not provide sufficient conductive material extendinguninterruptedly outward from the primary-surface material to the tip ofeach fin. Therefore, slots orientated parallel with the longitudinallength of element 10,

must be regulated in length so as to provide sufficient segments 14extending uniterruptedly outward from the primary-surface material toeffectively and efficiently transfer heat from one medium in theenclosed channel to a medium external of the channel. Depending on theend use application of a heat exchanger employing the finned element ofthis invention, any artisan can easily determine the length of the slotsnecessary to provide sufficient conductive paths normal to thelongitudinal axis of the heat exchange element. Thus the slots can bedisposed anywhere between and 180 with respect to the longitudinal axisof the heat exchange element provided it yields an angle of approachsuitable for a particular end use heat exchange applicatron.

FIGS. 2, 2A and 2B show two isocompression heat exchange channels 21,22, having front fins 23 and 24, respectively, and rear fins 25 and 26,respectively, juxtaposed in touching relationship with projected buttons27 and 28 in contact. This two channel assembly is sufficient to showthe dual set of passages that conventional heat exchangers have.Passages 29 in channel elements 21 and 22 define one set of confinedpassages independent of, and separate from, a second set of passages 30formed between adjacent elements 21 and 22. One fluid, shown as solidline arrows, can be fed through passages 29 while simultaneously, asecond cooler fluid, shown as broken line arrows, can be fed throughpassages 30 to effectively cause a transfer of heat from the hotterfluid to the cooler fluid without having them intermixed. The fluidpassing through the passages 30 will first pass through slattedapertures 31 and 32 in front fins 23 and 24, respectively, therebyeffecting a transfer of the heat which was conducted along the fins 23and 24, from the primary-surface area 33 and 34, respectively. Likewise,when the fluid medium leaves passages 30 through apertures 35 and 36 inrear fins 25 and 26, respectively, it again effects a transfer of heatwhich was conducted along the fins 25 and 26 from the primary-surfacearea 37 and 38, respectively.

To illustrate an embodiment of the heat exchange elements of thisinvention, FIG. 3 shows a partial exploded isometric view of anautomobile radiator 41 employing such heat exchange elements 42. Anarray of heat exchange'channel elements 42, having front fins 43 andrear fins 44, and aligned so that their isocompression projected buttonsare arranged such that they extend outward from each wall of a pair andcooperate with similar projected buttons on the wall of a second pair soas to space apart the walls of a pair to form passages between adjacentchannel elements. For clarity of illustration, FIG. 3F shows the sideview of two elements 42 with the fins 43 and 44 removed therebydisplaying the touching relationship of isocompression projections 45,and passages 46.-Note that the isocompression projections 45 are notaligned on opposite walls of the pair that comprises element 42, but areoffset, or non-symmetrically disposed, on such opposite walls of thepair. FIG. 3E shows an embodiment where the projections 45' aresymmetrically disposed on opposite walls ofa pair of each element A sideview of an end of element 42 and front fin 43 is shown in FIG. 3C whileFIG. 3A shows the side view of the opposite end of element 42 and rearfin 44. Fin 43 is shown with slats 47 at about a 45 angle (slot angle a)with respect to the longitudinal edge of element 42. As shown in FIG.3B, apertures 49 are disposed between slats 47 of front fin 43 and arealigned so that a medium flowing normal to the longitudinal length ofthe assembled elements 42 would flow through such apertures 49 withsubstantially mimimum resistance. Stated another way, the medium flowpath across the slats 47 will be substantially minimized by thealignment of the slats in an orientation substantially parallel to thedirectional flow of such medium. Although not shown, rear fins 44 havethe same type apertures between slats 48 as shown for fins 43. Member 50is placed on top of the array of elements 42 and then support bracket 51is placed over the assembly along the finless channel edge segments 4shown in FIG. I. This arrangement provides stability for the array ofelements 42 in addition to securing proper alignment for elements 42.Support bracket 51 must have an outer plate segment 52 adaptable forsecuring header 53 thereon, and in addition, it must be capable ofproviding a leak-tight seal to header 53 and to the channel elements 42so that in the operational mode, a fluid fed through the elements 42 viaheader 53 will not leak into the space between adjacent elements 42. Asimilar type header, not shown, is positioned at the opposite end ofelements 42 to provide a compact efficient automobile radiator.

An alternate embodiment for the elements of this invention would be tohave two fins, 54 and 55, disposed from the same longitudinal edge 56 ofelement 42" as shown in FIG. 3D. The fins could be an extension of thewalls of the primary-surface material or they could be added separatelyas shown. It is to be understood that more than two fins from the sameedge could be provided to yield a multiple fin constructed channel. Afinned heat exchange element made by extending the primary-surface wallsfore and aft from the enclosed channel segment, or by separately addingthe fin between the mating wall edges of the enclosed channel segments,can have the mating wall edges bonded into a seam joint as for exampleby ultrasonic welding.

Although the fins of this invention are intended as an improvement onall channel type heat exchangers and primary-surface heat exchangers,the following example will be directed to the use of such fin in anautomobile radiator which will illustrate the basic efficiency and otheradvantages derived from the use of such fins.

EXAMPLE Three one-square-foot, heat exchange frontal area isostressradiators, two finless and one finned, constructed as shown in FIG. 3,along with three conventional type copper radiators, typified by theradiator shown in FIG. 4 and modified to one-square-foot, heat exchangefrontal area size, were tested in a wind tunnel shown schematically inFIG. 5. The prime function of the test was to measure and compare theheat transfer capacity of the different type heat exchangers. This wasaccomplished by pumping heated coolant through the test radiators as afixed rate as shown in FIG. 6 while varying the air flow rate as shownin FIG. 5. As shown in FIG. 6, steam was fed from a supply source (notshown) through a feedback control valve through a 0-to-30 psi. gauge 81.The steam was controlled by valve 82, parallel coupled to a fineradjustment valve 83, before being fed into a water heater tank 84. Thepressure in the tank 84 was measured by a 0-60 psi. gauge 85. The wateroutput from the tank 84 was fed into a test radiator 86 and upon exitingfrom the radiator 86, the water was pumped by motor 87 via parallelcoupled control valve 88 and series control valve 89 back into theheater tank 84. A water meter 90 was connected downstream of the pump 87so as to measure the water flow through the radiator 86. Steamcondensate in the tank 84 was discharged into a recepticle, not shown.The feed rate of the heated coolant through the radiator was thuscontrolled at all times, and although not shown, temperature measuringdevice were used to record the temperature of the water into and out ofthe radiator.

The test schematic of FIG. shows a wind tunnel used to regulate the rateand temperature of an air flow through the passages formed betweenadjacent heat exchange elements in the radiators being tested. Airentering the tunnel was first passed through a calibrated orifice 60,which measured the air volume flow into a four cubic foot plenum chamber61, and then fed through flow straightening screens 62 into a taperedadapter section 63. The adapter section 63 was provided to effect asmooth transition in the air flow between the plenum chamber 62 and a lsquare foot wind tunnel duct 64 coupled to a test radiator 65. A blower(not shown) was positioned downstream of the radiator for controllingthe air flow through the radiator. The heated air from radiator 65 waseither exhausted via camper 66 or recirculated into the test room viadamper 67 so as to provide a degree of temperature control within theroom. To reduce the air flow rate through the radiator, control damper68 was coupled downstream of the exiting air flow from radiator 65. Thetapered adapter section 63 and the flow straightening screens 62 weresuccessful in keeping velocity variation through the test radiator 65 ata minimum. Velocity profiles and pitot tube readings made over thefrontal area of different test radiator 65 indicated that air velocityvariation for all the radiators tested was within i 5 percent. One0-to-2 inch manometer 69, and two 0-to-4 inch manometers 70 werepositioned as shown in the test circuit and used to measure the airpressure drop. Two grids, 72 and 73, containing four thermocouples, eachof which was placed in the center of one quarter of the flow passagearea of the radiator 65, measured the average inlet and exit airtemperature through test radiator 65. A Brown multipoint chart recorder(not shown) and a Rubicon potentiometer (not shown) were coupled to thegrids and recorded the termocouple readings. Thus, an accurate testcircuit was provided for measuring the heat transfer capacity of thetest radiators.

lsocompression test radiator number 1, similar to that shown in FIG. 2,except it was finless, was fabricated by pressing the right" and leftchannel halves of aluminum between male and female epoxy isocompressiondies prepared as described in my aboveidentified patent application. Theisocompression impressed channel halves were then trimmed and foldedlongitudinally on the edge, whereupon they were degreased, acid cleanedand Alodine treated, followed by a water rinse. After drying, anadhesive known as Resin Type EA-9 l 4, manufactured by Hysol Division ofDexter Corporation, Calif, was applied to the 13 inch long folded edgeon each channel half, and mating channel halves were then joined to forma [.625 wide channel. The channel was then placed in a fixture androlled seam tight. After removing the excess adhesive from the channel,the adhesive in the seam was oven cured. Thereafter spacers wereinserted into the tube and an adhesive was applied to each of theprojected buttons and the tube walls. Inserts were inserted at the tubeends and an array of ten channels were clamped in touching relationshipin a fixture and then the adhesive was oven cured. Thereafter the arrayof channels were again cleaned as specified above and then assembledinto a header as shown in FIG. 3. Once again adhesive was used to sealthe channels to the header thus providing a test radiator.

lsocompression test radiator number 2 was prepared similar to the aboveexcept that the projected buttons were not adhesively secured together.The width of the channels measured 1.9 inches, and the length was 13inches.

lsocompression test radiator number 3 was prepared similar to testradiator number 2 except that the seams were welded, and slotted finswere disposed on the fore and aft longitudinal edges of the channel, asshown in FIG. 3. The overall width of the channel measured 1.7 inchesand the unbent fins measured 0.2 inch and 0.5 inch at the fore and aftlongitudinal edges. The length of the channel measured 13 inches. Theslot angles a and a measured 45, the slat angle ,8 and B measured 40 andthe bending angles 'y and y varied for six fin configurations asfollows:

Three similar type conventional automobile radiators, test numbers 4, 5and 6, typical copper core consisting of brass tubes soldered to thincopper fins, except for varying fin and tankage configurations, weremodified to one square foot heat exchange frontal area by cutting thecore and reinstalling a shortened header and tank. Thus all testradiators were designed to yield one square foot heat exchange frontalarea. The finned isostress test radiator cost substantially less to makethan the conventional copperbrass test radiators because in the former,the cost of the base metal material was less per pound than the basemetal material of the latter.

The nominal test conditions for the various radiators are shown inTable 1. Of the conventional radiators tested, test radiator 4 was foundto be superior on a heat transfer per unit of air horsepower basis. Thusradiator 4 was compared to test radiators l, 2 and 3.

TABLE l-Contlnued TEMPERATURE FLOW RATE NUM- INLET INLET BER TEST OF AlRWATER AIR WATER NO. RUNS "F. F. CFM CFM 8 90 190 600-2000 17 5 s 90 200600-1900 14 s 90 210 600-2100 17 8 75 1 5 60t-2000 4 e s 90 2 651-2500 71 1s 90 2 0 401-1250 7 2 3 16 90 210 400-2000 17 T e 1 a 75 1x5 600-180014 Type 2 x 75 1145 600-1800 14 T e 3 x 75 1115 600-2000 14 Type 4 a 751x5 600-2000 14 Type 5 s 75 1x5 600-2000 14 T e a s 80 1145 600-2050 14FIG. 7 shows a plot of capacity vs. air volume flow rate for the testradiators 1 through 4. The conditions for the plot was 100F. averagecoolant fluid to inlet air temperature difference, using a 50-50Prestone water coolant at a flow rate of between 14-17 gallons perminute. As illustrated in FIG. 7, radiator 3 Type 5 had a highercapacity for the same air volume of flow rate than the best conventionaltype radiator, radiator 4.

The result of this test proved that the finned aluminum radiator of thisinvention will perform comparably to the best conventional automobileradiator and cost substantially less to make because of optimum metalutilization. Thus this invention provides economical, compact,light-weight, finned heat exchange channel elements that can beassembled into an efficient heat exchanger for various applications.

Iterative calculations based on the experimental data of the test forradiator 3 in its various configurations revealed the following:

Heat Transfer Coefficient, BTUIFt F Hr. Low Speed (600 FPM High Speed(1200 FPM Approach Speed) Approach Velocity) Primary Secondary PrimarySecondary Surface Surface Surface Surface Type 1 20.2 13.7 30.6 20.6Type I 20.3 23.0 30.5 39.3 Type 3 20.2 18.6 30.7 34.0 T e 4 20.2 27.030.5 47.0 Type 5 211.4 31.5 30.3 53.0 Type 6 20.4 30.5 30.6 52.0

Thus a radiator having a front tin with the same bent angle 7 of about30 as the rear fin, provided the best embodiment for an automobileradiator using the specific type heat exchange channel elements tested.

A radiator similar to that shown in FIG. 3 and constructed as specifiedfor test Radiator 3 Type 5 was installed in an automobile and whensubjected to local driving conditions, the radiator performed admirably.

along at least one longitudinal section of the channel element, said finhaving a multitude of slatted apertures arranged in a louverconfiguration with adjacent slats separated by slot-shaped apertures,having the fin angle between about 0 and about 60 wherein y is the angleformed between the plane of the fin and a plane containing the maximumdimension width line and longitudinal length line of said channelelement, slat width of at least 0.02 inch and less than 0.10 inch, theslat angle B is between about 15 and about wherein B is the angle formedbetween the plane of the fin and the plane of the slats and the slotangle a is between about 0 and about wherein a is the angle formedbetween the longitudinal length line of the channel and the longitudinallength line of the slots.

2. The heat exchanger of claim 1 wherein at least two of such channelelements are aligned and spaced apart to provide a dual set of passages,the first set of passages defined by, and bound within, the conductivewalls of each channel element, and a second set of passages defined by,and disposed between, adjacent channels, said fins being disposed at thefore and aftsections of the channel elements, and said section definedas the remote sections of the channel element as measured from a planecontaining the center points of two adjacent channel elements and thelongitudinal axis of the channel.

3. The heat exchanger in claim 2 wherein the slotted fin is fabricatedwith an angle of approach 0 of between 0 and 70, said angle of approach0 being defined as the angle between a first line which is parallel to aplane containing the maximum dimensional width line and the longitudinaldimensional length line of the channel element and perpendicular to thechannels longitudinal length line, and a second line formed by theintersection of a plane onto the surface of a slat on the slotted fin,said plane being normal to the surface of the slatand containing thefirst line as defined above.

4. The heat exchanger of claim 3 wherein said angle of approach isbetween 0 and 45.

5. The heat exchanger of claim 2 wherein more than one slotted fin isdisposed substantially along a longitudinal section of the channelelement.

6. The heat exchanger of claim 4 for use in conjunction with internalcombustion engines wherein said channel elements are flat aluminumisocompression channels, wherein the channel elements are aligned suchthat-the planes of each element which contains the maximum dimensionalwidth line and longitudinal length line of such elements are parallel;and wherein the angle of approach is between about 0 and about 45 theprimary-surface channel elements.

7: The heat exchanger of claim 6 wherein the maxi- UNITED STATES PATENTOFFICE IIQRTIF'ICATE- OF CORRECTION Patent No. 3,8'45,8l 1 I Dated November 5, 197 4 Leslie 0. mm

' Inventor(s It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 1, delete "continuing" and substitute cc nta1ning--'-. I

Columh9, line 62, after "element,. insert l2-- Signed and sealed this7th de'y of anuar 1975.

('SEAL) Attest McCOY H. GIBSON JR. '3 v I c; MARSHALL DANN Attesting.Officer Commissioner of Patents Pat 212 4. 7'4

1. A heat exchanger comprising at least one flat primary-surface heatexchange channel element formed and bound by at least one thermallyconductive walled material with a maximum dimension width line and alongitudinal length line, said element having an entrance opening and anexit opening, the improvement which comprises the addition of at leastone secondary-surface heat exchange slotted fin of width greater than0.1 inch and less than 0.6 inch disposed substantially along at leastone longitudinal section of the channel element, said fin having amultitude of slatted apertures arranged in a louver configuration withadjacent slats separated by slot-shaped apertures, having the fin anglegamma between about 0* and about 60* wherein gamma is the angle formedbetween the plane of the fin and a plane containing the maximumdimension width line and longitudinal length line of said channelelement, slat width of at least 0.02 inch and less than 0.10 inch, theslat angle Beta is between about 15* and about 90* wherein Beta is theangle formed between the plane of the fin and the plane of the slats andthe slot angle Alpha is between about 0* and about 180* wherein Alpha isthe angle formed between the longitudinal length line of the channel andthe longitudinal length line of the slots.
 2. The heat exchanger ofclaim 1 wherein at least two of such channel elements are aligned andspaced apart to provide a dual set of passages, the first set ofpassages defined bY, and bound within, the conductive walls of eachchannel element, and a second set of passages defined by, and disposedbetween, adjacent channels, said fins being disposed at the fore and aftsections of the channel elements, and said section defined as the remotesections of the channel element as measured from a plane containing thecenter points of two adjacent channel elements and the longitudinal axisof the channel.
 3. The heat exchanger in claim 2 wherein the slotted finis fabricated with an angle of approach theta of between 0* and 70*,said angle of approach theta being defined as the angle between a firstline which is parallel to a plane containing the maximum dimensionalwidth line and the longitudinal dimensional length line of the channelelement and perpendicular to the channel''s longitudinal length line,and a second line formed by the intersection of a plane onto the surfaceof a slat on the slotted fin, said plane being normal to the surface ofthe slat and containing the first line as defined above.
 4. The heatexchanger of claim 3 wherein said angle of approach is between 0* and45*.
 5. The heat exchanger of claim 2 wherein more than one slotted finis disposed substantially along a longitudinal section of the channelelement.
 6. The heat exchanger of claim 4 for use in conjunction withinternal combustion engines wherein said channel elements are flataluminum isocompression channels, wherein the channel elements arealigned such that the planes of each element which contains the maximumdimensional width line and longitudinal length line of such elements areparallel; and wherein the angle of approach is between about 0* andabout 45*.
 7. The heat exchanger of claim 6 wherein the maximumdimensional width line of each primary-surface channel element isbetween about 0.75 inch and 2.0 inches.
 8. The heat exchanger of claim 6wherein angle Beta is between about 30* and about 60*; angle Alpha isbetween about 45* and about 135*; and angle gamma is between about 0*and about 60*.
 9. The heat exchanger of claim 6 wherein the fins are anextension of the walls of the primary-surface channel elements.
 10. Theheat exchanger of claim 6 wherein the fins are separately added betweenthe longitudinal edges of the primary-surface channel elements.